1. Field of the Invention
This invention relates generally to the field of wireless network protocols and processes. More particularly, the invention relates to an apparatus and method for reducing congestion on a wireless network.
2. Description of the Related Art
A variety of wireless data processing devices currently exist including standard cellular phones, cellular phones equipped with data processing capabilities, wireless personal digital assistants (“PDAs”) such as the Palm® VIIx handheld, and, more recently, corporate wireless messaging devices such as the Blackberry™ wireless pager developed by Research In Motion (“RIM”).™
In operation, some of these wireless devices will attempt to lock on to a base station from which it receives the highest signal strength, commonly referred to as the Received Signal Strength Indication (“RSSI”). Referring to FIG. 1, the wireless device 120 will periodically evaluate the RSSI received from each of a plurality of surrounding base stations 110-112 and will generally select the base station having the highest RSSI value. Accordingly, a device in motion (e.g., in a car during a user's daily commute) will tend to jump from one base station to another based on the continually changing RSSI values. For example, if base station 110 is close to the user's home, the user's wireless device 120 may initially lock on to that base station 110 when the user leaves for work, based on the strength of the RSSI value (identified as “RSSI 1”). As the user commutes to work, however, the wireless device 120 may jump to a new base station 112 as the RSSI value received from that base station 112 (identified as RSSI 3) become greater than the initial RSSI value by some pre-defined margin.
Because each wireless device is programmed to select a base station based on RSSI, certain powerful ‘wide-area’ base stations located in highly populated areas may tend to become overloaded (e.g., such as those located near the intersection of several major freeways or high-rise office buildings). This can be so despite the addition of dedicated ‘campus’ bases, which don't always attract the localised devices they are meant to serve, due to their lower output power. This problem is graphically illustrated in FIG. 2 which shows three coverage areas 210, 220, and 230 associated with three base stations 211, 221, and 231, respectively. Area 240 falls within the coverage areas of all three base stations. However, if RSSI values within area 240 measured from base station 231 are higher than RSSI values measured from the other two base stations 211 and 221, then wireless devices will tend to select base station 231 from within area 240. If area 240 is significantly more populated than surrounding areas, this may cause base station 231 to become overloaded. In this situation, it would be desirable to reallocate a certain number of devices to the alternate base stations 211 and 221.
Accordingly, what is needed is an improved base station selection algorithm for a wireless device. What is also needed is a selection algorithm which will factor in variables other than RSSI when making base station selection decisions (e.g., such as the current load on each base station).